dt-bindings: mfd: twl: Fix example

Fix example to also conform to rules specified in the separate
not-included gpadc binding.

Fixes: 62e4f339 ("dt-bindings: regulator: twl-regulator: convert to yaml")
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reported-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Lee Jones <lee@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20240612134039.1089839-1-andreas@kemnade.infoSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/mfd/ti,twl.yaml

@@ -225,6 +225,7 @@ examples:
         gpadc {
           compatible = "ti,twl6030-gpadc";
           interrupts = <6>;
+          #io-channel-cells = <1>;
         };
 
         rtc {